brain correlates of discourse processing: an fmri ... · the literal and the nonliteral meaning...

Neuropsychologia 44 (2006) 2348–2359

Brain correlates of discourse processing: An fMRI investigationof irony and conventional metaphor comprehension

Zohar Eviatar a,∗, Marcel Adam Just b

a Institute of Information Processing and Decision Making, Psychology Department, University of Haifa, Haifa 31905, Israelb Center for Cognitive Brain Imaging, Carnegie-Mellon University, United States

Received 26 August 2005; received in revised form 30 April 2006; accepted 4 May 2006Available online 23 June 2006

Abstract

Higher levels of discourse processing evoke patterns of cognition and brain activation that extend beyond the literal comprehension of sentences.We used fMRI to examine brain activation patterns while 16 healthy participants read brief three-sentence stories that concluded with either aliteral, metaphoric, or ironic sentence. The fMRI images acquired during the reading of the critical sentence revealed a selective response of thebrain to the two types of nonliteral utterances. Metaphoric utterances resulted in significantly higher levels of activation in the left inferior frontalglrc©

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yrus and in bilateral inferior temporal cortex than the literal and ironic utterances. Ironic statements resulted in significantly higher activationevels than literal statements in the right superior and middle temporal gyri, with metaphoric statements resulting in intermediate levels in theseegions. The findings show differential hemispheric sensitivity to these aspects of figurative language, and are relevant to models of the functionalortical architecture of language processing in connected discourse.

2006 Elsevier Ltd. All rights reserved.

eywords: Figurative language; Irony; Metaphor; Pragmatics; fMRI

. Introduction

Scholars of language pragmatics and discourse have longeen interested in the manner in which people understand theeanings of utterances that are not intended literally but ratherguratively. For example, Gibbs (1994) makes an eloquent argu-ent that irony is a common form of thought (and not just

anguage) because it is a method for juxtaposing one’s expecta-ions with the realities of life, and treating the discrepancy withome general approach to life, such as humor or bitterness ornowingness. Irony is one of the lenses through which we seehe world, and through which we describe the world to others.imilarly, metaphor is a way of understanding one concept in

erms of another, transferring knowledge from one domain tonother, in ourselves and in those with whom we communi-ate. The comprehension of both irony and metaphor requireson-literal interpretation that extends beyond first-order lexi-al and syntactic processing. For example, irony and metaphor

∗ Corresponding author. Tel.: +972 4 824 9668; fax: +972 4 824 0966.

both require that the comprehender know something about thespeaker’s beliefs and intentions and use that knowledge in gen-erating the non-literal interpretation.

In the last decades, studies of the functional architecture oflinguistic abilities in the brain have examined the relative abil-ities of the two cerebral hemispheres, and have revealed thatalthough the left hemisphere (LH) is dominant for the majorityof language functions, the right hemisphere (RH) is involvedin the processes of narrative construction (e.g. Gernsbacher &Robertson, 1999) and discourse representation (e.g. Kuperberget al., 2000; Long & Baynes, 2002). The involvement of the RHin the processing of verbal irony (e.g. McDonald, 2000), con-ventional and novel metaphors (e.g. Rapp, Leube, Erb, Grodd,& Kircher, 2004; Sotillo et al., 2005), and predictive and coher-ence inferences (Beeman, Bowden, & Gernsbacher, 2000) havebeen examined. The present study examined patterns of activa-tion levels as measured by fMRI in the brain while participantswere reading utterances that differed in their discourse value: lit-eral, conventional metaphors, and irony. The empirical questionunder investigation here has two parts: first, does the processingof literal and nonliteral statements result in activation of the same

E-mail address: [email protected] (Z. Eviatar). brain areas? Second, will the distribution of activation be the

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Z. Eviatar, M.A. Just / Neuropsychologia 44 (2006) 2348–2359 2349

same for two types of figurative language, irony and metaphor?The theoretical goal is to formulate new, testable hypotheses(based on the empirical findings) concerning the roles of theparticipating cortical areas in the two hemispheres in the com-prehension of figurative language.

1.1. Pragmatic models of the comprehension of figurativelanguage

In general, theories of pragmatics have conceptualized bothtypes of nonliteral language in terms of similar mechanisms. Thestandard pragmatic model (Grice, 1975; Searle, 1979) proposedthat both violate the truthfulness maxim, signaling the compre-hender that the utterance requires more than literal processing.Metaphoric utterances need not be literally true1 (a politicianis not literally a lightning rod), whereas ironic statements arefalsified by the context (the hearer knows that it is raining heav-ily, when the speaker says, ‘What a great day for a picnic’). Formetaphors, the incoherence of the statement is solved by relatingthe attributes of the vehicle (the lightning rod) to those of thetarget. For irony, coherent interpretation requires understandingthat the speaker is pretending, and actually intending a meaningopposite of what they are saying. There is nothing inherentlyfigurative about the statement ‘What a great day for a picnic’,except the fact that it cannot be true in the context of heavy rain.The position of the standard model of pragmatics is that the lit-er

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iar (‘frozen’ or ‘dead’) metaphors and ironies may be processedlike very long ambiguous words. Our results will not be able toaddress the issues of timing, given the low temporal resolution offMRI, but they will be able to address the issue of localization.Thus, for both types of figurative language, we will comparethe distribution of activations with metaphoric and ironic state-ments to that found for literal statements, but we will not be ableto discern differential effects of context.

Although most models posit that irony and metaphor are simi-lar in some respects, there are also important differences betweenthe two non-literal forms. Sperber and Wilson (1995) have pro-posed that metaphor is a descriptive use of language that involvesa relationship between the propositional form of an utterance andthe thought that it is representing. Irony is more interpretive andcomplex, in that it involves a relationship between the thoughtsof the speaker and the thoughts of someone else (e.g., by alludingto the failure of shared expectations or the violation of norms, asproposed by Kumon-Nakamura, Glucksberg, & Brown, 1995).One source of empirical evidence for the differences betweenirony and metaphor is found in developmental studies of normalchildren. These studies have found that metaphors are compre-hended at an earlier age than ironies (Bara & Bucciarelli, 1998;Happe, 1993; Winner, 1988). Apparently, the comprehension ofirony is related to the sophistication of theory-of-mind mecha-nisms, because children and adults who are able to make correctattributions of first order false beliefs (to model what another per-sssasTaa

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ral interpretation of the utterance is always processed, and theneprocessed in order for the correct meaning to be extracted.

This standard model has been repeatedly disconfirmed byndings that response times to conventional metaphors and

ronies are not slower than to literal statements (e.g. Giora,997). More recent models have proposed that under someircumstances both types of meaning may be processed concur-ently, without computing the literal meaning of the expressionrst (Colston & Gibbs, 2002; Gernsbacher, Keysar, Robertson,

Werner, 2001; Gibbs, 2001; Giora, 1999). The majority ofodels propose that a common mechanism is used to com-

rehend both literal and nonliteral language, where ironies andetaphors are seen as a source of polysemy in a language (e.g.acciari & Glucksberg, 1994). Thus, the timeline of compre-ension of these utterances may resemble the process of lexicalccess for ambiguous words (e.g. Swinney, 1979), with bothhe literal and the nonliteral meaning activated initially, and thenappropriate meaning inhibited as a result of the effects of con-ext. An active field of research examines this timeline, and thenteraction of lexical and contextual effects on the activation ofiteral and nonliteral meanings (e.g. Peleg, Giora, & Fein, 2001;u, Kellas, Metcalf, & Herman, 2000; Colston & Gibbs, 2002).iora (1999) has emphasized the importance of the lexicaliza-

ion of nonliteral language, showing that in terms of her gradedalience hypothesis, salience is determined first and foremost byhe lexical status of the utterance. According to this view, famil-

1 We adhered to the argument that metaphors and similes assert the sameelationship between vehicle and topic, and some of our metaphoric sentencesere technically similes, in that they included the words ‘like’ or ‘as’. Seeppendix A. We refer to both as metaphors in the article.

on knows) are able to comprehend metaphors, but not ironictatements. Children and adults who are able to make correctecond order attributions (to model what another person knowsbout what a third person knows) are able to comprehend ironictatements (Winner, Brownell, Happe, Blum, & Pincus, 1998).his relative difficulty of irony over metaphor persists over time,s Colston and Gibbs (2002) have shown that it takes healthydults longer to read ironic than metaphoric statements.

.2. Neuropsychological models

Neuropsychological models of the comprehension of non-iteral language are based on data from a variety of paradigms.he classic studies indicate that an intact RH is necessary forfficient processing of metaphors and connotations (Brownell,otter, Meichelow, & Gardner, 1984; Brownell, Simpson,ihrle, Potter, & Gardner, 1990; Winner & Gardner, 1977).ore recent studies using tasks involving different discourse

rocesses have revealed dissociations in populations with brainamage, where irony comprehension may be deficient, butetaphors are comprehended relatively better, or vice versa,

n different patients (Langdon, Davies, & Coltheart, 2002).here is some relation between lesion locus and comprehen-ion deficit (right hemisphere lesions impair irony compre-ension more than metaphor comprehension; left hemisphereesions impair metaphor comprehension more than irony com-rehension (Giora, Zaidel, Soroker, Batori, & Kasher, 2000;cDonald, 2000)), supporting the hypothesis that there may

e distinguishable brain substrates associated with such pro-essing. However, a clear-cut consistent specialization of theH for the processing of figurative language with unilaterally

2350 Z. Eviatar, M.A. Just / Neuropsychologia 44 (2006) 2348–2359

brain-damaged patients has not been found (e.g. Klepousniotou& Baum, 2005; Tompkins, 1990). Importantly, recent studiesof the pragmatic abilities of patients with agenesis of the cor-pus callosum have shown that although they have intact rightand left hemispheres, and are able to transfer semantic informa-tion (probably via the anterior commissure), as shown in intactStroop interference, they are deficient in the comprehension ofboth emotional prosody and conventional metaphors (Paul, VanLancker-Sidtis, Schieffer, Dietrich, & Brown, 2003). Given therelationship between emotional processing and irony compre-hension, and the fact that these participants made no errors onliteral phrases, these authors suggested that interhemisphericintegration of higher order processes is necessary for the pro-cessing of non-literal language.

The hypothesis that the RH is involved in ‘coarse’ seman-tic coding (Beeman, 1998) and in the processing of alternativemeanings of ambiguous words has been examined using dividedvisual field paradigms with normal participants. These studieshave suggested that the RH is less efficient than the LH at sup-pressing the inappropriate meaning of an ambiguous word (Faust& Gernsbacher, 1996), and seems insensitive to dominance, fre-quency, and context in the process of lexical access (Coney& Evans, 2000; Faust & Chiarello, 1998). However, specificRH sensitivity to the metaphoric meanings of words with thisparadigm has had an uneven history of replication (Anaki, Faust,& Kravetz, 1998; Faust & Weisper, 2000).

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contradicts the context: His dad said, “Thanks for keeping yourpromise”. The underlined statements were being read during thefMRI data acquisition. The full list of stimuli is in the appendix.We expected to see the effects of the common mechanisms inthe comprehension of these three types of statements, whichshould evoke the classical language areas in the left hemisphere,together with differences, either in the pattern of left hemisphereactivation, or in right hemisphere participation, resulting fromthe distinguishing processes for metaphor and irony. The moregeneral goal was to use the discovery of the neural bases of thesediscourse processes to enrich the psychological characterizationof the figurative comprehension processes.

2. Methods

Participants read brief stories ending in either a literal, metaphoric, or ironicstatement. We used fMRI in an event related design to measure brain activationwhile the participants were reading the final, critical sentence.

2.1. Participants

The participants were 16 right-handed students (7 female) at Carnegie-Mellon University who were paid for their participation and signed IRB-approved informed consent forms.

2.2. Materials

The stories consisted of three sentences. The first two sentences consti-tuted the context for the third sentence, which was always a literal, ironic, ormttwmssro2aFfam

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Thus, behavioral studies with patients and intact participantsave suggested that damage in both hemispheres can give riseo deficits in the processing of figurative language, and thatigher order interhemispheric integration may be necessary forhese processes. The growing number of functional imagingtudies of language processing support such a conclusion (seeookheimer, 2002 for a review). Specifically, many studies have

evealed RH activations in fMRI studies while participants haveeen doing many linguistic tasks. RH activations are most ofteneen when participants must make causal inferences or discourseevel computations (e.g. Bottini et al., 1994; Caplan & Dapretto,001; Ferstl & von Cramon, 2001; St. George, Kutas, Martinez,

Sereno, 1999).In sum, there is a large amount of behavioral evidence

rom normal and brain-damaged populations to indicate thatronic, metaphoric, and literal statements are processed differ-ntly. However, the functional organization of these processess unclear. Our study compared brain activation in the conditionhere individuals were reading statements in which it was clear

hat the speaker literally meant what they said versus conditionsn which it was clear that they were speaking either metaphor-cally or ironically. The metaphors that were presented werell conventional or ‘frozen’ metaphors that were not ironic. Forxample, given the context: John bragged to Amy that he couldun very fast. They had a race and he left her far behind. Theetaphoric statement that follows this excerpt is appropriate to

he context: Amy said, “You are like greased lightning”. In addi-ion, all of the ironies were non-metaphoric. That is, the characterlways said the opposite of what they meant. Thus, consider theontext, George promised to be quiet in the library. He got inrouble for talking very loudly. The ironic statement that follows

etaphoric statement made by one of the characters in the story. The final sen-ence was followed by a simple yes/no comprehension question, to ensure thathey were attending to the content of the stories. There were 9 stories of each type,ith the 27 stories presented in a random order. Two versions of the stimulusaterials were used (differing slightly to fit different types of final statements)

o that type of final statement was not confounded with the story content. In aeparate norming study, 20 participants who were not in the imaging experimentead the stories and classified the final statements as literal, metaphorical, ironic,r other. Half of these norming participants read Version 1 and half read Version. For Version 1, 94% (for literal statements), 93% (for metaphoric statements),nd 96% (for ironic statements) of the participants agreed with our classification.or Version 2, 88%, 87% and 88% agreed with our classification respectively,or literal, metaphoric, and ironic statements. Both versions are listed in theppendix, together with the proportion of participants who classified the state-ent according to our categories.

A comprehension question followed each of the stories (see below), whichsked about the true state of beliefs of the speaker. For example, in the story abouthe race between John and Amy, the question was: ‘Does Amy think John runsaster than her?’, and the participant had to press a button for ‘yes’ or ‘no’. Thus,e insured that the participants understood what the speaker really thought, even

f their utterance was metaphoric or ironic (e.g., the opposite of what they reallyhought). It may be argued that we cannot know that our participants processedhe metaphoric statements, but given that these were healthy university students,nd that the metaphors were all familiar ones, and that the pretest was done onhe same population, we feel confident that the critical figurative statements werenderstood as such.

.3. Procedure

The first two sentences of each story were presented together for 5 s, followedy a 3 s blank period. The third, critical sentence appeared next for 5 s, followedy a 7 s blank period. Finally, a 4 s period containing the comprehension probeuestion followed. Fig. 1 shows the timings of the story presentation. Five 20 sxation periods were interspersed among the stories, one at the beginning, and

hen every seven stories. These fixation presentations were used as baselinectivation levels for the computations described below. Stories that were notollowed by a 20 s fixation period were instead followed by a 7 s rest period. Only


Fig. 1. Stimulus presentation timing in single trial.

items in which the participant answered the question correctly were included(no participant made more than two errors). Approximately a day or two beforescanning, the participants were familiarized with the task using different stimulusmaterials.

2.4. Imaging procedures

The fMRI data were collected using a GE Medical Systems 3.0T scanner atthe Magnetic Resonance Research Center of the University of Pittsburgh Med-ical Center. A commercial birdcage, quadrature-drive radio-frequency wholehead coil was used. The study was performed with a gradient echo, reso-nant echo planar pulse sequence with TR = 1000 ms, TE = 18 ms and a 70◦ flipangle. Sixteen oblique-axial slices were imaged, and each slice was 3 mm thickwith a gap of 1 mm between slices. The acquisition matrix was 128 × 64 with3.125 mm × 3.125 mm × 3 mm voxels. Structural images for anatomic local-ization were taken in the axial plane and then resliced to correspond to thefunctional images. They were a 124-slice SPGR volume scan with TR = 25 ms,TE = 4 ms. The acquisition matrix was 256 × 256, with 1.5 mm slice thickness.Image preprocessing (including baseline correction, de-ghosting, mean correc-tion, motion correction, and trend correction) was performed using FIASCO(Eddy, Fitzgerald, Genovese, Mockus, & Noll, 1996; Lazar, Eddy, Genovese,& Welling, 2001). The mean of the maximum head motion for each participantdid not exceed .3 voxels. Participants whose data exceeded this criterion wereexcluded.

2.5. fMRI analyses

To compare the amount of activation in each participating cortical areaacross conditions, 19 anatomically defined ROIs were drawn for each participantusing the parcellation scheme described by Rademacher, Galaburda, Kennedy,Fact(tdp

Castanon, Ghosh, Tourville, & Guenther, 2003), and the resulting assessment ineach ROI can be averaged over participants and compared across conditions.

The central fMRI data for each item came from 5 images obtained for 5 s(at a rate of 1 image per sec), starting from 6 s after the exposure of the criti-cal statement, to allow for the hemodynamic response delay (Bandettini, Wong,Hinks, Tokofsky, & Hyde, 1992). There were nine such intervals (1 per story)in each experimental condition, resulting in 45 images per condition per partic-ipant. These were compared to the 100 images per participant obtained duringthe five 20 s fixation intervals, which constituted our baseline measures. Thedata analysis quantified BOLD-contrast-related changes in the fMRI-measuredsignal using a dependent measure which takes into account both the volumeof activation and the percentage change in signal relative to a fixation baselinelevel (Xiong, Rao, Gao, Woldorff, & Fox, 1998). These two dependent mea-sures typically both show effects of cognitive manipulations. For each voxel inthe a priori defined ROIs, the intensity of signal in an experimental conditionwas compared to that for the fixation condition using a t-test with a threshold oft > 5.0, a high threshold that is similar in conservativeness to a Bonferroni cor-rection for multiple comparisons. The sum of the percentage change in signal

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ilipek, and Caviness (1992) and further refined by Caviness, Meyer, Makris,nd Kennedy (1996), as shown in Fig. 2. These ROIs are intended to include anyognitively related areas in which at least some participants produced activa-ion. The ROIs were defined independently by two highly trained staff memberswith an inter-rater reliability of .84 in previous studies) for each individual par-icipant and any discrepancies were systematically resolved. The use of a prioriefined anatomical ROIs allows the activation volume to be assessed within eacharticipant’s native brain space without any morphing-induced distortion (Nieto-

ig. 2. Schematic of the eight lateralized ROI definitions per hemisphereadapted from the Caviness et al. (1996) parcellation scheme. The ROI labelsre explained in Table 1.


intensity was then calculated for each ROI and each condition by cumulating thechange in signal intensity (relative to the baseline) across voxels that reached thecritical threshold for that condition. Thus for each ROI, for each experimentalcondition, the mean (over 16 participants) sum % change in signal intensity (andthe count of activated voxels) reflected the amount of difference in the BOLDcontrast-related changes between that experimental condition and the baseline.

3. Results

Within each ROI, a one-way ANOVA tested for the effect ofthe type of critical utterance (literal, ironic, or metaphoric) on themeasure of activation (mean sum signal intensity) across the 16participants. Six regions of interest across the two hemispheresrevealed differential effects of statement type, and thereforesubsequent analyses focused on these regions. The results areshown in Table 1, with those areas showing reliable outcomes ofplanned comparisons highlighted in gray. (The analyses usingthe number of activated voxels as the dependent variable (thesemeans are shown in parentheses in Table 1) yielded slightlyweaker versions of the same patterns as did the analyses usingsum signal intensity. Therefore, only the latter are further dis-cussed.)

In three regions in the left hemisphere, the inferior frontalgyrus (IFG), the inferior temporal gyrus (IT), and the inferior

extrastriate cortex (IES), the activation for metaphoric state-ments was significantly greater than for the other types ofstatements, as shown in Table 1. Planned comparisons weremade between the mean % signal change in the three exper-imental conditions within each of these regions. The F-ratioscomparing metaphoric versus literal statements were: in IFGF(1, 15) = 7.43, p < .01; in IT: F(1, 15) = 5.84, p < .05; and inIES: F(1, 15) = 7.96, p < .01. The F-ratios comparing metaphoricversus ironic statements were: in IFG F(1, 15) = 4.15, p < .05; inIT F(1, 15) = 4.51, p = .05; and in IES F(1, 15) = 3.86, p < .06).These results are shown in Fig. 3.

Two areas showed reliable effects of statement type in theright hemisphere, as shown in Table 1. The right superior andmiddle temporal region revealed higher activation levels forironic statements than for literal statements, F(1, 15) = 5.21,p < .05; metaphoric statements resulted in intermediate values.In the right inferior temporal gyrus (RH IT), the effect wasthe same as the one in the left inferior temporal gyrus (LHIT), but much smaller in magnitude. Although levels of acti-vation are attenuated in the RH (a reflection of left hemisphericspecialization for this linguistic task), the activation levels formetaphors are significantly higher than for the other types ofstatements (metaphoric versus literal statements: F(1, 15) = 5.23,

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ean sum % change in signal intensity (and number of activated voxels) and T

he regions containing significantly different amounts of activation are shaded.Centroids (centers of mass) of activation in each ROI are group averages of individualre presented for only the metaphor condition because they were similar in the other

ch coordinates of activation in each ROI condition

participants’ centroids which were morphed into Talairach space. The centroidsconditions.


Fig. 3. Five brain regions showing differential effects of the type of critical utterance in the sum of % signal intensity. The upper three graphs show differentialeffects of metaphoric statements vs. literal and ironic statements. The graphs in the bottom row show differential effects of ironic statements vs. literal and metaphoricstatements. The error bars are based on the mean S.E. derived from the ANOVAs.

p < .05; metaphoric versus ironic statements: F(1, 15) = 5.29,p < .05).

Another left hemisphere area, the intraparietal sulcus (IPS),showed higher activation for metaphor than for irony, but theliteral statements produced an intermediate level of activation.It may be that metaphoric and literal interpretation both entailsome degree of visual imagery, resulting in IPS activity duringsentence comprehension (Just, Newman, Keller, McEleney, &Carpenter, 2004). By contrast, irony may be more of a seman-tic/logical mode than a visual transformation, hence there wouldbe less IPS activity. Fig. 4 illustrates all of these patterns in thesurface rendering of the group activation, as well as in one axialslice.

4. Discussion

We have shown that the three types of statements all resultedin activation of the classical language areas in the LH, indicatingconsistency with previous imaging studies of language com-prehension. At the same time, metaphoric statements resultedin significantly higher activation levels than ironic and literalstatements in three of the regions, the left inferior frontal gyrus,the left inferior temporal gyrus, and the left inferior extrastri-ate region. Two different areas in the right temporal lobe weredifferentially sensitive to irony and metaphor: ironic statementsresulted in differential activation levels in the right superior andmiddle temporal gyri, while metaphoric statements resulted in


Fig. 4. (a) Group activation (averaged over 16 participants’ t-maps) of brain regions in the three experimental conditions, showing more left-hemisphere activationin the metaphor than the irony and literal conditions in several LH regions (x-coordinate = 43), and more right-hemisphere activation (x-coordinate = −46) in thetemporal area for the irony condition than the other conditions. The statistical threshold for all of the analyses was t = 5.0. (b) Example of one participant’s activationin left IFG in each of the three experimental conditions.

relatively higher activation levels in the inferior temporal gyrus.These results support the position that figurative language isprocessed by the same general mechanism as literal statements,but also that irony and metaphor processing have distinguishingcharacteristics.

4.1. Metaphor

The finding of higher activations in the left IFG and inferiortemporal regions for metaphors replicates the finding reportedby Rapp et al. (2004), and converges with hypotheses that thisarea is involved in semantic selection (e.g. Keller, Carpenter, &Just, 2001). Variations of models of metaphor comprehensionusually involve some kind of comparison between the subjectof the metaphor and the vehicle, which is done by selection ofthe salient features of the vehicle to be compared to the subject(that is, Mary is as sharp as a razor because being smart islike being sharp (Glucksberg, 1998)). Another type of modelsuggests that the relations between the subject and the vehicle are

categorical (Glucksberg & Keysar, 1990), such that the subjectbecomes a member of a transient category exemplified by thevehicle (Mary is a sharp razor). In both types of models, themeanings of frequently used metaphors (such as the ones usedin this study) are lexicalized. The lexical contents of the phrase‘sharp as a razor’ includes, in addition to the literal meaning, themore abstract meaning of ‘smartness’. Thus, the comprehensionof these metaphors relies on lexical selection processes, whichare subserved at least in part by the left IFG (Keller et al., 2001).

The new results bear a sensible relation to two previousimaging studies of metaphor processing, Bottini et al. (1994)and Rapp et al. (2004). Both of these previous studies usednovel metaphors, whereas we used conventional, or idiomaticmetaphors. Bottini et al. asked participants to judge whether themetaphors were plausible or not, and Rapp et al. asked theirparticipants to judge whether their metaphors had a positive ornegative connotation. Interestingly, Bottini et al. found differ-ential RH activation for metaphor processing in inferior frontalgyrus, middle temporal gyrus, and precuneous, whereas Rapp


et al. found higher activation for metaphoric versus literal sen-tences in the same areas that we did: LH inferior frontal gyrus andinferior temporal gyrus. It is important to examine the similari-ties and differences between the three studies in our evaluationof the results. The differences are at many levels. Bottini et al.used PET imaging and a block design, while Rapp et al. andthe present study both used fMRI and an event-related design.It may be that these procedural differences underlie some ofthe differences among the results. However, the most importantdifference is that both previous studies used novel metaphors,whereas we used conventional metaphors.

Several theorists (e.g. Giora, 1999) have suggested that noveland conventional metaphors are processed differently, and someof our own research in progress strongly confirms this pro-posal. Specifically, the suggestion has been that novel metaphorsrequire computation of the relations between the vehicle and thesubject of the metaphor, whereas conventional metaphors arelexicalized, and are actually like long words, whose meaningis accessed as a unit. Thus, one would expect that the previoustwo studies would pattern together. In explaining the differencesbetween their study and that of Bottini et al., Rapp et al. sug-gested several sources of difference, other than the technology(PET versus fMRI) and design. Specifically, they suggest thatthe task, judging the plausibility of the metaphors, together withthe higher complexity of stimuli, resulted in the recruitmentof RH resources in the Bottini et al. study and not in theirs.Ttssihstwtmnisorw

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visual representation of a metaphor (Winner & Gardner, 1977),or grouping pairs of words according to perceived similarity(Brownell et al., 1984, 1990). Another possible reason for RHactivation during novel metaphor comprehension is that qual-itatively different processes are recruited, possibly involvinga search through coarse-coded information. Both accounts arealso supported by the findings of Kuperberg et al. (2000), whofound that sentences that violated semantic restrictions (e.g.,the semantic properties of the verb were incompatible with thesemantic properties of the object noun—‘the young man drankthe guitar’) resulted in higher activation in the right superior andmiddle temporal gyri, whereas sentences in which the violationwas syntactic (the young man slept the guitar) did not. Regard-less of the role of the RH in novel metaphor comprehension,these previous results are all consistent with the contention thatthe left IFG and temporal regions are involved in lexical access,and that conventional metaphors such as ours are accessed aslexical items.

We also saw that the inferior temporal gyrus in the right hemi-sphere showed the same pattern as the inferior temporal gyrus inthe left hemisphere. These data suggest that RH temporal regionsare recruited when plausibility is computed, semantic judgmentsare made, or more generally, as we show below, when the struc-ture of the whole narrative is processed, when the discourse isironic.

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his is because although the task in their study, judging whetherhe metaphor has a positive or a negative connotation, requiredemantic processing, it was independent of the lexical relation-hip of the nouns within the sentence. In the Bottini et al. study,mplausible metaphors violated the semantic properties of theead nouns, e.g., ‘the investors were trams’. In our study, thetimuli were complex, in that they were stories. However, all ofhe metaphors were both apt and conventional, such that theyere plausible in the context of the stories. Thus, it may be that

he critical difference between the study that found RH involve-ent in metaphor comprehension and the two studies that did

ot, is the necessity to evaluate the context of metaphor. Thats, when the task involves lexical access of the words in theentence, as with the simple metaphors of Rapp et al., or withur lexicalized metaphors, we see LH activations, and when itequires a higher level of analysis, as in a plausibility decision,e see recruitment of RH regions.There may be more than one reason that RH regions are acti-

ated during the processing of novel metaphors. Because we didot study such metaphors, we have no new data to offer here.owever, one possibility is that RH regions are recruited when

he task is made more difficult, by requiring the participants toake some sort of metalinguistic judgment about the stimuli.or example, Sotillo et al. (2005) reported ERP generators of

he N400 in a novel metaphor comprehension task in the rightuperior temporal gyrus, but the task also required participantso judged if a following word was related to the metaphor. Thelassic neuropsychological patient studies that found deficits inetaphoric processing in RH damaged patients relative to LH

amaged patients also required high-level judgments in addi-ion to the comprehension, such as judging the suitability of a

.2. Irony

Our results support the hypothesis that the RH is differentiallynvolved in the comprehension of irony. More specifically, it maye that the processing of irony can be related to the processingf communicative intent or the construction of a coherent nar-ative. The literal interpretation of an ironic utterance makes noense in its context. The involvement of the RH in the compre-ension of narratives has been suggested by patient studies, anday be related to the ability of the participants to understand the

peaker’s communicative intent (in the terms of relevance theorySperber & Wilson, 1995)) as dissociated from their informa-ive intent. In the literal and metaphoric conditions of our studyhere was no such dissociation: if the hearer could correctlyategorize the subject of the metaphor as a member of the cate-ory defined by the vehicle (as in Glucksberg’s (1998) model),hen they knew that the speaker meant what they said. In theronic condition however, it had to be clear that the speaker waspretending’—that is, not meaning what they said. This coulde computed by processing the coherence of the critical utter-nce in the context of the whole story. Robertson et al. (2000)eported higher levels of fMRI activation in the right middleemporal gyrus in an fMRI study in which participants readeries of unconnected sentences that they formed into narratives.eeman et al. (2000) showed that predictive inferences are acti-ated in the RH, and suggested that this is a reflection of coarseemantic coding in the RH. These findings together converge touggest recruitment of RH regions, when discourse processingequires construction of relations between separated entities inhe utterance, to make inferences or to compute plausibility oroherence.


A number of imaging studies have suggested that medialfrontal regions, particularly the paracingulate gyrus, are acti-vated when participants are performing tasks that rely on Theoryof Mind processing (see Gallagher & Frith, 2003 for a review).As the bottom of Table 1 indicates, activation in this area (SMFP,for superior medial frontal paracingulate) was high for all threetypes of utterances, and was not sensitive to utterance type. Thisarea has been proposed to subserve the process in which ‘. . . cuesare used in a particular way; that is, to determine an agent’smental state, such as a belief, that is decoupled from reality, andto handle, simultaneously these two perspectives of the world’(Gallagher & Frith, 2003, p.79). It may be the case that becauseall of the stories were followed by a question about the truesituation (e.g., was Ann’s dress clean or not, see Fig. 1), partic-ipants computed the mental state of the characters in all of thestories.

5. Conclusions

Our results converge with reports of the performance ofparticipants with unilateral brain damage on tests of sarcasmand metaphor comprehension. Giora et al. (2000) reported thatpatients with unilateral brain damage in the RH achieved lowerscores than patients with unilateral LH damage on a test of sar-casm comprehension, and higher scores than patients with uni-lateral LH damage on a test of metaphor comprehension. Thus,ttsruta

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asymmetry itself is likely subject to modulation by the charac-teristics of the comprehension task. In general, fMRI studies arerepeatedly demonstrating that laterality of activation is a dynam-ically determined property of the processing in the task, as aremany other aspects of activation. Which factors dynamicallydetermine the degree of laterality in activation and in controlof processing in specific tasks is an extremely interesting set ofissues for future research.

Acknowledgements

This work was partly supported by the National Institute ofMental Health, Grant MH-29617. We thank Rachel Giora forcomments on an earlier draft of the paper.

Appendix A

Stimuli used in the experiment. Half the participants sawVersion 1 and half saw Version 2. Preliminary analyses revealedno differences between the versions, such that the results werepooled across version. The numbers next to each question are thepercentage of participants in the norming study who classifiedit as we did. Items in bold type were being read in the imagedinterval.

V
he RH is differentially implicated in irony comprehension, andhe LH is differentially implicated in metaphor comprehen-ion. However, we also showed activation patterns in differentegions of the right temporal lobe, for ironic and metaphorictterances, supporting the hypothesis that within the RH, thesewo types of statements require the recruitment of differentreas.
Our findings converge with a large number of results of func-ional neuroimaging studies that support a view of brain functionn networks of brain regions that work together to constitute theunctional architecture of the mind. Specifically, as shown inig. 4a, all of our stimuli activated the classical perisylvian lan-uage regions. However, both ironic and metaphoric statementsesulted in extra activation in addition to this basic pattern: ironictatements resulted in the addition of a RH temporal region,nd metaphoric statements resulted in a larger volume in leftFG being activated above threshold. Just, Carpenter, Keller,ddy, and Thulborn (1996) proposed that functional networksf brain regions that function together to subserve a cognitiverocess are dynamic, such that added complexity in the cog-itive process results in the conscription of additional brainreas to the networks. The results of the present experimenteveal that the type of complexity (irony or metaphoric lan-uage) affects the location of brain regions that are added to theetwork.

It may be surprising from some perspectives to find thathere was not more activation in RH than LH for both ironynd metaphor processing. Although processing of both types ofgurative language has been characterized as a RH function, it isore likely that it is a bilateral function, with asymmetry in the

mount of activation in the two hemispheres. The degree of this

ersion 1Literal items

Johnny went on a hike with his brother. Suddenly he saw ahuge snake next to his foot

He said, “I am so scared” 90%Jim cleaned the backyard all day. He didn’t take any breaksMother said, “Jim, maybe you should eat something” 90%Joe’s little brother fell and hurt his knee. Joe washed it and put

a band-aid on itHis brother said, “You are so nice to me” 100%Betsy and Mary were on the basketball team. Mary scored a

lot of points in the gameBetsy said, “Mary is a great player” 90%Jack was talking on the phone. Sally and Mary came in very

quietlyJack said, “I didn’t notice you were here” 100%Betty and Laura were in the same class. Laura finished her

homework before BettyLaura said, “You sure are a slow worker” 90%Harry waited in line for 3 h to see the movie. He enjoyed

himselfHe said, “That was worth waiting for” 100%Ms. Jones asked the class to be very quiet. They got a prize for

being the best-behaved classShe said, “Thanks for listening to me” 100%Jim beat everyone in the class in chess. Harry introduced Jim

to the new teacherHe said, “Jim is our best chess player” 90%

Metaphoric itemsIn the morning John came to work early. He started to work

right away at a fast paceHis boss said, “John is a hurricane” 90%Father asked Mary to help him set the table. She sang a song

as she put all the plates in their placesFather said, “You are my sunshine” 100%Mary got straight A’s on her report card. Her parents were

proud of her


They said, “You are as sharp as a razor” 100%Susie helped her mom when her brother got sick. She took

good care of himHer mom said, “You are an angel from heaven” 90%Tom and Mike planned to go on a picnic. In the morning the

sun was shiningTom said, “It’s a golden day” 90%Larry told Sally that he knew how to cook. He gave her a taste

of his wonderful stewSally said, “This is heaven” 100%Lilly enjoyed herself at the movies. Jane asked her about the

movieLilly said, “I laughed my head off” 90%Donna was always late for everything. Today she made it

home on time for supperHer dad said, “You have turned over a new leaf” 90%Laura was out sick for a week. Johnny called her every dayLaura said, “You are a mother hen” 90%

Ironic itemsJane hates eggplant. Her mother prepared a big eggplant salad

for supperJane said, “Oh wow, my favorite food” 100%George went to Betty’s birthday party. Only two other people

cameHe said, “It is really crowded here” 100%Tommy worked hard in the garden. His brother threw leaves at

himTommy said, “Thanks for all your help” 90%Ken was worried about having his hair cut. When the barber

finished, Ken looked terrible

V

His dad said, “Thanks for keeping your promise” 100%Donna was always late. Her parents bought her a new watch,

and she was on time for supperHer dad said, “I’m glad we got you a watch” 100%Mary couldn’t sleep after seeing the movie. She told John

about itShe said, “It was just too exciting for me” 80%Laura was out sick for a week. Johnny called her every dayLaura said, “Thanks for worrying about me” 90%

Metaphoric itemsGeorge went to Betty’s birthday party. Fifty people crowded

into her small apartmentHe said, “I feel like a sardine” 90%Jim ate a big lunch with three desserts. When he finished he

asked for moreMom said, “Jim, you are a bottomless pit” 90%Jack was talking on the phone. Sally and Mary came in very

quietlyJack said, “You are as quiet as mice” 80%Betty and Laura were in the same class. Laura finished her

homework before BettyLaura said, “You work like a snail” 80%Ken was worried about having his hair cut. When the barber

finished, Ken’s ears stuck outHe said, “You’ve turned me into a clown” 90%John bragged to Amy that he could run faster than Amy. They

had a race and he left her far behindAmy said, “You are like greased lightning” 90%Ann promised to keep her party dress clean. She came home

covered in mud
He said, “Thanks for the great haircut” 100%John bragged that he could run faster than Amy. They had a
race and she left him far behindShe said, “You sure are faster than me” 90%Ann promised to keep her party dress clean. She came home

covered in mudHer mom said, “Thanks for staying so clean” 90%George promised to be quiet in the library. He got in trouble

for talking very loudlyHis dad said, “Thanks for keeping your promise” 100%At the restaurant Mark said he wasn’t hungry. He ordered only

coffee and ate all of Ed’s friesEd said, “I can see you’re not hungry” 100%Mary fell asleep during the movie. John woke her up at the endShe said, “It was just too exciting for me” 90%

ersion 2Literal items

Jane loves chicken. Her mother prepared roast chicken forsupper

Jane said, “Oh wow, my favorite food” 80%Father asked Mary to help him set the table. She sang a song

as she put all the plates and silverware in their placesFather said, “You are really helping me” 90%Mary got straight A’s on her report card. Her parents were

proud of herThey said, “What a smart girl you are!” 100%Tommy worked hard in the garden. His brother came and

raked the leavesTommy said, “Thanks for all your help” 80%”Susie helped her mom when her brother got sick. She took

good care of himHer mom said, “You deserve a prize” 70%George promised to be quiet in the library. He sat in a corner

looking at a book

Her mom said, “You are a dirt magnet” 90%At the restaurant Mark said he wasn’t hungry. He ordered only

coffee and ate all of Ed’s friesEd said, “You’re like a vacuum cleaner” 90%Ms. Jones asked the class to be very quiet. The principal

yelled at them for making noiseShe said, “I feel like I’m talking to the walls” 80%

Ironic itemsJohnny’s little sister was mad at him. When she tried to hit him

Johnny laughed at herHe said, “I am so scared” 90%In the morning John came to work late. He immediately

decided to take a breakHis boss said, “Don’t work so hard” 90%Joe’s little brother fell and hurt his knee. Joe laughed and

didn’t help him get upHis brother said, “You are so nice to me” 90%Betsy and Mary were on the basketball team. They lost the

game when Mary missed all her shotsBetsy said, “Mary is a great player” 70%Tom and Mike planned to go on a picnic. In the morning it was

raining very hardTom said, “Great weather for a picnic” 90%Larry told Sally that he knew how to cook. When she tasted

his watery stew, it was awfulSally said, “You sure are a great cook” 80%Lilly was nervous walking alone at night. Her brother sneaked

up and scared herLilly said, “Very funny” 100%Harry waited in line for 3 h to see the movie. It was very boringHe said, “That was worth waiting for” 90%Jim lost all the chess games he ever played. Harry introduced

Jim to the new teacherHarry said, “Jim is our best chess player” 90%


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